Certification to EN 13432:2000 or ASTM D6400-19 is a precondition for municipal organic waste collection programs, and home-compostable caddy liner claims typically require the TÜV Austria OK compost Home specification in addition. The compound Ecomp 120 is processed as a 100% monolayer for 15–25 µm dry-flow applications, but for wet organic waste with puncturing risk, a certified aliphatic-aromatic copolyester such as PBAT is let down at 10–30 wt%; this shifts Elmendorf tear from below 15 g to above 50 g when measured under ASTM D1922-15 and delays pinhole formation in folded corners. Drying to a residual moisture level below 250 ppm is mandatory, which requires a desiccant dryer with a dew point of -40°C or lower and a residence time of 4 h at 80°C before extrusion. The preferred extruder for blown film is a single-screw machine with a 24:1 to 30:1 L/D ratio, barrier flights, a Maddock mixer section, and a compression ratio of 2.5:1 to 3.5:1; a screen changer with a 100/200/325/200/100 mesh arrangement is used to remove carbonized particles that can cause melt fracture at thin gauges.

During blown film conversion, melt temperature at the die lip is held at 190–205°C with a die gap of 0.8–1.2 mm and a blow-up ratio of 2.5:1 to 3.5:1. Frost line height is maintained at 4–8 die diameters; if the frost line rises or falls outside this band, machine-direction gauge bands appear and tear propagates from the fold edge. On cast film lines, chill rolls set to 18–25°C and vacuum box pinned edges prevent neck-in; however, film surface temperature above 50°C at the secondary nip triggers blocking unless 0.5–1.5 wt% synthetic silica anti-block masterbatch with a 5–7 µm particle size is used. Terminal articles include 10 L, 20 L, and 30 L kitchen caddy liners, certified organic waste sacks, and thin produce roll bags. Sealing is carried out on impulse machines at 120–130°C and 0.2–0.4 MPa jaw pressure to avoid melt-through at thicknesses below 25 µm. Storage of finished rolls above 40°C and 60% RH causes hygroscopic expansion, loss of tensile modulus, and seal strength drift.

What process control hierarchy governs agricultural mulch film disintegration?

Under EN 17033:2018, biodegradable mulch film must prove 90% biodegradation within 24 months in cold soil, a condition that is materially different from industrial compost certification under ISO 14855-1:2012. A monolayer of Ecomp 120 alone is often insufficient at 15°C soil temperature because the abiotic hydrolysis of PLA slows at low ambient temperatures, and published data for pure PLA films meeting the EN 17033 cold-soil criterion is limited. Commercial agricultural formulations therefore contain 65–80 wt% Ecomp 120 with 20–35 wt% PBAT or a starch-based aliphatic-aromatic copolyester, plus 3–8 wt% carbon black masterbatch for UV screening in black film grades. White or black/silver dual-layer constructions add a second white masterbatch layer at 4–6 wt% titanium dioxide to reflect photosynthetically active radiation toward crop rows.

The mulch structure is usually cast on a 1.2–2.2 m wide flat die at 8–15 µm final thickness with melt temperature capped at 190–200°C to limit lactide reformation that later migrates to the soil-film interface and changes wetting behavior. Chill rolls are set to 20–30°C; higher roll temperatures produce die lines and uneven gauge. In blown film, the blow-up ratio is kept between 2.0:1 and 3.0:1 because the low melt strength of highly loaded PLA blends causes bubble sag at wider ratios. Field failure is dominated by premature fragmentation along the crop row where UV exposure and mechanical abrasion combine, so tensile retention after simulated weathering and tear propagation resistance according to ISO 6383-2:1983 must remain above 40% of the unexposed film before the harvest removal window. Terminal products include black biodegradable mulches for tomato, pepper, and cucurbit production, as well as clear or white mulch for strawberry and leafy green soil warming. Soil incorporation after the season is permitted only when the certificate matches field biodegradation data for the specific geographic soil temperature profile; aerobic compost certification alone does not automatically satisfy this requirement.

Where high clarity and deadfold dominate the property ranking, the compound is processed into cast film for transparent produce bags and bakery window applications. The finished films require migration testing under EU 10/2011 with overall migration below 10 mg/dm² and specific migration limits for any slip or anti-block additives; for US-market food contact, FDA 21 CFR 176.170 covers PLA as a component of food-contact films, but residual lactide and tin catalyst levels in the final article must be verified. Ecomp 120 is typically run at 100% for 15–30 µm clear film; heat seal initiation is reduced from 120–130°C to 95–110°C by blending 5–15 wt% of a low-melting biodegradable copolyester. Optical grades use 0.5–1.5 wt% synthetic silica anti-block masterbatch; above 2.0 wt%, haze rises above 5% and transparency becomes unacceptable for fresh produce display. Oxygen permeability at 23°C and 0% RH for PLA film is around 3.5 cm³·mm/m²·day·atm; water vapor transmission rate under ASTM E96/E96M-21 at 38°C and 90% RH is approximately 5 g·mm/m²·day for a 100% film, but these values shift upward when PBAT or plasticizer is introduced.

Cast film extrusion uses a 0.4–0.6 mm die gap, 195–205°C melt temperature, 18–25°C chrome roll temperatures, and line speeds from 150 to 300 m/min depending on gauge. Transverse thickness variation is controlled with a beta or X-ray sensor to ±2% to avoid blocking and print registration errors. The tensile modulus of PLA in the 3.0–3.5 GPa range creates higher deadfold retention than low-density polyethylene, so the film is used for twist wrap and clear sleeves where shape retention is desired. Terminal articles include compostable produce roll bags, bakery window pouches, floral wrap, and over-wrap for tea boxes. Service temperature is limited to 55°C; hot fill, steam retort, or microwave exposure is outside the operating envelope because the film softens and may distort under load.

Laminated Film Construction and Seal Integrity in Compostable Mailer Envelopes

For mailer envelopes in the 50–100 µm thickness range, monolayer Ecomp 120 film has high stiffness but insufficient slow-puncture resistance for distribution abrasion. Blending with 10–25 wt% PBAT or polybutylene succinate raises slow-puncture energy under ISO 7765-1:1988 and reduces brittle fold cracking at the side seals. White mailers require 4–8 wt% titanium dioxide masterbatch; titanium dioxide increases opacity but may lower elongation at break if the masterbatch carrier resin is incompatible with PLA, so batch-to-batch carrier resin compatibility testing is conducted before full production. Film converted into envelopes is usually coextruded on a three-layer die with an A/B/A structure, where the core contains the higher PBAT content and the skins are neat compound to support sealing and print adhesion.

Compliance is evaluated under EN 13432:2000 and ASTM D6400-19, but the adhesive strip and label facestock must also be compostable; suitable adhesives include starch-based or compostable hot melts with a softening point below 65°C to avoid blocking in warm transport. Extrusion uses a die gap of 1.2–1.8 mm, melt temperature of 190–205°C, and blow-up ratio of 2.0:1 to 3.0:1; corona treatment to 40–50 dyne/cm is applied inline before water-based or UV flexo printing. Terminal products include e-commerce polymailers, garment bags, and document envelopes. Automatic bag converting requires a film coefficient of friction below 0.35 against metal and heat seal strength above 8 N/15 mm according to ASTM F88/F88M-21; without these values, machine jams occur at the wicket fold and peel-open failures occur in customer handling.

When tackifier migration is excluded from cast film, pressure-sensitive label facestock becomes technically viable

Compostable pressure-sensitive label facestock produced from the compound is restricted to ambient-temperature labeling because PLA loses dimensional stability above 55°C. The film is cast onto a paper liner and coated with a compostable pressure-sensitive adhesive, but tackifier migration from the adhesive into PLA causes softening and hazing. To control this, the film surface is corona-treated to 48–52 dyne/cm before adhesive coating, and a water-based primer acts as a barrier between the adhesive and PLA. Compliance for the complete label construction requires certification under EN 13432:2000 and disintegration testing according to ISO 14855-1:2012; the adhesive must not exceed 5 wt% of the total label to avoid heavy metal and ecotoxicity failures. The facestock is processed at 100% or with 1–2 wt% slip masterbatch for release, with die gap 0.5 mm, melt temperature 195–205°C, and chill roll temperature 20°C.

The main converting conflict is film blocking at the winder when roll tension exceeds 0.4 N/mm width; for 20 µm facestock, tension is tapered to less than 0.3 N/mm to avoid layer-to-layer adhesion. Terminal products include compostable label facestock for fresh produce tags, paperboard packaging labels, and UV-inkjet printed direct thermal labels. Service temperature for roll storage is limited to 35°C; prolonged exposure above this range accelerates surface tack development and can shift the adhesive release properties. Published data for this specific label configuration is limited, so converting trials are required to define the exact primer coat weight and adhesive selection for each liner type.